The invention relates to a holding apparatus adapted for electrostatically holding a component, in particular a silicon wafer. The invention relates also to a method for producing the holding apparatus. Applications of the invention are in the provision of devices or tools for holding components by means of electrostatic forces, in particular for holding semiconductor components, for example silicon wafers.
Holding apparatuses for holding components electrostatically, which are also referred to as electrostatic holding apparatuses, electrostatic clamping apparatuses, electrostatic clamps, ESCs or electrostatic chucks, are known in general. An important application of electrostatic holding apparatuses is in holding silicon wafers in lithographic semiconductor processing, for example in chip production, in which the particular advantages of electrostatic holding, such as the ease of switching of electrostatic holding or clamping forces, a high positioning accuracy and the reliable fixing of silicon wafers, are exploited.
Typically, an electrostatic holding apparatus has a structure having a plurality of plate-type or layer-type elements that perform differing functions (see e.g. U.S. Pat. No. 4,502,094 or U.S. Pat. No. 8,476,167). At least one plate-type element is equipped with an electrode device with which the electrostatic holding forces are generated. According to U.S. Pat. No. 8,476,167, the electrode device comprises a plurality of electrodes which are embedded between the plate-type elements. Furthermore, an electrostatic holding apparatus typically has at least on its upper side a plurality of projecting upper burls which form a support surface for the silicon wafer.
A conventional electrostatic holding apparatus having embedded electrodes, for example according to U.S. Pat. No. 8,476,167, has the following disadvantages. Because the electrostatic holding force depends on the distance between the silicon wafer and the electrodes, burls having as small a height as possible (e.g. <10 μm) are used to generate a high holding force. However, this leads to an increase in the sensitivity to unwanted particles, which may not find sufficient space between the burls and can impair the planarity of the silicon wafer support. Alternatively, the holding force can be increased by increasing the electrode voltage, but this is associated with risks relating to electrical breakdowns or other faults. Furthermore, because the electrodes are arranged in the spaces between the burls, the silicon wafer that is held can be deformed to an undesirably high degree between the bearing contact points. There can be further disadvantages in relation to the thermal and mechanical coupling of the silicon wafer that is held. For example, the silicon wafer can tend to slip sideways along the extent of the support surface despite a high holding force.
The mentioned disadvantages occur not only in the case of electrostatic holding apparatuses for silicon wafers, but also in the case of holding apparatuses having embedded electrodes for other components, such as, for example, for glass plates having a transparent electrode (ITO), which form AMLCD substrates.